Molecule Beam Epitaxy Research Articles

Epitaxial growth of Er 2O 3 films on oxidized Si(111) and Si(001) substrates

The crystalline structures and morphologies of Er 2O 3 films epitaxially grown on both oxidized and clean Si surfaces are investigated by X-ray diffraction, in situ reflection high energy electron diffraction and atomic force microscopy. Both crystallinity and surface roughness of Er 2O 3 films grown on oxidized Si substrates are improved compared to those grown on the corresponding clean ones, indicating that the oxidized Si surfaces are favorable to the epitaxial growth of Er 2O 3 films compared with the clean ones. At the same time, the oxidized Si surface can suppress the formation of Er silicide at the interface during the film growth, which is preferable for epitaxial Er 2O 3 films with smooth surfaces. Good epitaxial growth of Er 2O 3 films, with a surface mean roughness as small as 1.51 Å and good crystallinity as well, has been achieved on an oxidized Si(111) surface by molecule beam epitaxy.

Role of gallium wetting layer in high-quality ZnO growth on sapphire (0001) substrates

A Ga wetting layer was used to modify the surface structure of sapphire (0001) substrate to prepare high-quality ZnO film by radio frequency plasma-assisted molecule beam epitaxy. We found that this Ga layer plays a crucial role in eliminating 30° rotation domains, controlling polarity and decreasing defect density in ZnO epilayers, as demonstrated by in situ reflection high energy electron diffraction,ex situ high resolution X-ray diffraction and high resolution cross-sectional transmission electron microscopy. Zn-polar film of ZnO was determined by convergent beam electron diffraction. A Ga bilayer model is proposed to understand the effects of the Ga wetting layer on high-quality ZnO growth.

Realization of Low Threshold of InGaAs/InAlAs Quantum CascadeLaser

By optimizing the molecule beam epitaxy growth condition, thequality of quantum cascade (QC) material has greatly been improved. Thespectrum of double x-ray diffraction indicates that the interfacebetween the constituent layers is very smooth, the lattice mismatchbetween the epilayer and the substrate is less than 0.1%, and theperiodicity fluctuation of the active region is not more than 4.2%.The QC laser with the emission wavelength of about 5.1 µm is operated atthe threshold of 0.73 kA/cm2 at liquid nitrogen temperature withthe repetition rate of 10 kHz and at a duty cycle of 1%. Meanwhile,the performance of the laser can be improved with suitable post processtechniques such as the metallic ohmic contact technology.

Correlation of structural and optical investigation of InGaAs/InAlAs quantum cascade laser

Double X-ray diffraction has been used to investigate InGaAs/InAlAs quantum cascade (QC) laser grown on InP substrate by molecule beam epitaxy, by means of which, excellent lattice matching, the interface smoothness, the uniformity of the thickness and the composition of the epilayer are disclosed. What is more, these results are in good agreement with designed value. The largest lattice mismatch is within 0.18% and the intersubband absorption wavelength between two quantized energy levels is achieved at about λ= 5.1 μm at room temperature. At 77 K, the threshold density of the QC laser is less than 2.6 kA/cm 2 when the repetition rate is 5 kHz and the duty cycle is 1%.

Characterization of Co-catalyzed Multiwalled Carbon Nanotubes by High-Resolution Transmission Electron Microscopy

ABSTRACTThe dependence of characteristics of multiwalled carbon nanotubes (MWCNT) on the microstructure of cobalt catalysts are intensively investigated by high-resolution transmission electron microscopy (HREM). The cobalt catalysts are prepared by either molecule beam epitaxy (MBE) or by DC magnetron sputtering, followed by MWCNT growth by microwave plasma CVD. The MBE-grown Co thin films consist of large epitaxial grains, whereas the Co nanoparticles of FCC or HCP crystal structures can be directly grown on Si(001) substrates by sputtering. Various HREM technologies are applied to completely characterize the microstructures of those Co catalysts and MWCNT. The results reveal that the morphology and microstructures of MWCNT are greatly controlled by the characteristics of Co catalysts. Better quality of carbon nanotube can be grown by FCC cobalt rather than HCP cobalt. The different effects of cobalt catalysts on MWCNT are discussed in this paper.

Effects of annealing time and Si cap layer thickness on the Si/SiGe/Si heterostructures thermal stability

The effects of annealing time and Si cap layer thickness on the thermal stability of the Si/SiGe/Si heterostructures deposited by disilane and solid-Ge molecule beam epitaxy were investigated. It is found that in the same strain state of the SiGe layers the annealing time decreases with increasing Si cap layer thickness. This effect is analyzed by a force-balance theory and an equation has been obtained to characterize the relation between the annealing time and the Si cap layer thickness.

Epitaxially grown Fe/Ag ultrathin films on GaAs and their application to wideband microwave notch filter

Ultrathin ferromagnetic iron/silver films were epitaxially grown on GaAs substrates by molecule beam epitaxy. Sample magnetization and magnetic anisotropy were studied by magneto-optic Kerr effect experiment. The common features in the ferromagnetic resonance peak-to-peak linewidth ΔHpp are identified, with the narrowest linewidth of 23Oe. Electronically tunable wideband notch filters utilizing the flip-chip devices have been realized using Fe/Ag film-GaAs waveguide layer structures. The peak absorption carrier frequency of a propagating microwave has been tuned in a range from 9.6 to 21GHz in a modest magnetic field from 0 to 1650Oe for single layer structure. For multilayer structures, peak absorption is intensified with tuned range from 10.7 to 27GHz. The experimental results are in good agreement with the theoretical predictions for the case in which the magnetic field is applied along the easy axis of the Fe film.

Structural and Photoluminescence Characterization of GaN Film Grown on Si (111) Substrate

GaN epilayer grown on Si (111) substrate by a novel vacuum reaction method rather than metal organic chemical vapor deposition or molecule beam epitaxy is reported. Scanning electron micrograph shows that surface of GaN film is flat and crack-free. A pronounced GaN (0002) peak appears in the x-ray diffraction pattern. The full width at half-maximum (FWHM) of the double-crystal x-ray rocking curve for (0002) diffraction from the GaN epilayer is 30 arcmin. The photoluminescence spectrum shows that the GaN epilayer emits light at the wavelength of 365 nm with an FWHM of 8 nm (74.6 meV).

Optical Characterization of Heavily Carbon Doped GaAs

ABSTRACTOptical measurements have been performed on heavily carbon doped GaAs layers grown on semi-insulating GaAs substrates by MOMBE (metal-organic molecule beam epitaxy). Photoluminescence excitation (PLE) spectroscopy was used to measure the onsets of optical absorption in these GaAs:C epilayers. It was found that in samples with free carrier concentrations of 6.2×1019, 1.6×1020, and 4.1×1020cm−3, optical absorption begins at 1.40, 1.52, and 1.53 ev, respectively. Combined with the band gap narrowing data from photoluminescence (PL) spectra, we estimated Fermi level locations relative to the top of the valence band. We also measured reflectance in the near infrared region and estimated the effective mass of free holes using a classical two-oscillator model.